The present invention relates to a ball hitting tool testing device and more specifically to a testing device applicable to a ball-hitting tool such as a racket for tennis, badminton, squash, table tennis, a golf club, and a bat for baseball. In particular, the present invention relates to a testing device, which is preferably used for the tennis racket. With a robot gripping the tennis racket, the testing equipment device performs several motions of the tennis racket which is performed at the time of stroke by a person with the person gripping the tennis racket. Thereby the testing device allows quantitative evaluation of speed of the a ball at the time of a stroke, controllability, and spin performance.
Research has been made for a testing device of a ball-hitting tool such as the tennis racket so that the testing device has a function of hitting a ball in a state close to that in which a person actually hits the ball.
For example, the conventional testing device of the tennis racket is disclosed in the following books: Journal [No. 940-9] of the Japan Society of Mechanical Engineers, Symposium on AVD Lecture Papers, Page 128; Journal [No. 95-28] of the Japan Society of Mechanical Engineers, fourth meeting Symposium on Motion and Vibration Control Lecture Papers, Page 170; [No. 95-17] Journal of the Japan Society of Mechanical Engineers, Robotics and Mechatronics lecture, 1995 Lecture Papers (Vol.B), Page 1260; Journal [No.96-20] of the Japan Society of Mechanical Engineers, Symposium Lecture Papers, Page 35; and Nikkei Mechanical, May 15, 1995, No.454, Page 66.
The testing device of the tennis racket reported in the above-described books has a construction shown in FIG. 10. The testing equipment is designed by considering that when a person performs a ball-hitting motion, with the human gripping the tennis racket, the tennis racket makes a complicated motion which is a combination of a translation motion and a rotary motion. The testing equipment is a horizontal two-joint robot having a minimum necessary degree of freedom to allow the translation motion and the rotary motion to be accomplished.
That is, in the testing device, the motor 1 rotates (rotation on S-axis) the first joint 2 directly in a direction shown with an arrow, the first joint 2 is connected to one end of the connection plate 3, the second joint 4 is rotatably installed on the other end of the connection plate 3, the first joint 2 and the second joint 4 are interlocked with each other with the timing belt 5, and the motor 1 rotates (rotation on T-axis) the second joint 4 in a direction shown with an arrow. The holder 6 is fixed to the second joint 4, and the grip 8a of the tennis racket 8 is inserted into and fixed to the holder 6.
The testing device having the horizontal two joints is driven by one driving device (motor 1). The rotation of the first joint 2 (corresponding to person""s shoulder) on the S-axis and the rotation of the second joint 4 (corresponding to person""s wrist) on the T-axis are synchronous with each other. The testing device can reproduce a ball-hitting motion of the tennis racket at a volley time in playing tennis.
As shown in FIGS. 11 and 12, the holder 6 has the shock-absorbing rubber sheet 2 disposed on the inner peripheral surface of each of the fixing parts 1a and 1b each made by dividing a metal cylinder into halves. With the grip 21a of the tennis racket 20 sandwiched between the fixing parts 1a and 1b through the rubber sheet 2, the fixing parts 1a and 1b are clamped with the screw 3 to hold the tennis racket 10 thereby.
The testing device having two horizontal joints has been developed to measure the mechanical characteristic of the tennis racket at the time of a volley in playing tennis. Thus the tennis robot is capable of evaluating the performance of the tennis racket only at the time of the volley but is incapable of evaluating the performance of the tennis racket at the time of a stroke. In evaluating the performance of the tennis racket, the evaluation of speed of a ball, controllability, and spin performance at the time of the stroke are more important than the evaluation of the tennis racket at the time of the volley. As described above, since the conventional testing device has the horizontal two joints, it has a problem in that it is incapable of evaluating the performance of the tennis racket at the time of the stroke.
More specifically, a swing in tennis is made not in one swing plane but is varied because a player raises his/her body and lifts his/her arm. To spin a ball when the ball is served, it is necessary to angularly change the racket plane by inward rotating the arm. An effective volley can be made not only by hitting the ball with the racket plane vertical to the ground but also in combination of an angle change of the longitudinal axis of the racket to the ground by a vertical swing motion of the wrist and the outward rotation of the arm.
The testing, having two horizontal joints, shown in FIG. 10 is incapable of reproducing several motions including a rotation-accompanied vertical motion of the tennis racket following a motion of the upper part of a player""s body, a rotating motion of the tennis racket by a twist of the wrist caused by inward and outward rotation of the arm and a vertical motion of the wrist.
The collision speed of the tennis racket held by the testing device is as low as about 5 m/sec. Although description is made in the above-described books that the collision speed of the tennis racket held by the testing equipment is as high as 30 m/sec, the description is not substantiated.
The head speed of the tennis racket at the time of the stroke is 10-30 m/sec in regulation-ball tennis and 50 m/sec in softball tennis. The head speed of the tennis racket swung by a high-class player is faster by about 10 m/sec than that of the tennis racket swung by a beginner. The angular velocity of the high-class player""s wrist is faster by 700xc2x0/sec than that of the beginner""s wrist (page 70 through 77 of xe2x80x9cNew Science of Tennisxe2x80x9d published by tennis journal).
The most conspicuous difference in players"" swings is a swing speed and in particular the difference between swing speeds of wrists. Thus there is a demand that the testing equipment is capable of adjusting the head speed of the tennis racket in the range of 5-50 m/sec. However, as described above, since the collision speed in the testing equipment device is about 5 m/sec, the testing equipment is incapable of realizing a high head speed.
Depending on the high-class player and the beginner, the testing device is required to allow the rotation speed of the entire testing equipment and the rotation speed around the wrist to be freely adjusted. However, in the testing device shown in FIG. 10, since one motor drives the first joint and the second joint, the testing device is incapable of freely adjusting the rotation speed (rotation speed of the first joint) of the entire testing device and the rotation speed (rotation speed of the second joint) around the wrist independently and freely.
Further the holder 6, made of metal and rubber, used in the testing device shown in FIG. 10 is incapable of absorbing a shock and a strain applied to the holder 6 as a result of a collision between the tennis racket and the ball at the time of a high-speed swing. Thus in the case where the testing device conducts a ball-hitting test repeatedly, the tennis racket is broken at the shaft or the throat thereof.
The present invention has been made in view of the above-described problem. It is a first object of the present invention to provide a testing device, of a ball-hitting tool such as a tennis racket, which reproduces a motion of a tennis racket at the time of a stroke. It is a second object of the present invention to provide a testing device, which can adjust a ball collision speed from a low speed to a high speed and adjust a rotation-speed thereof and a rotation speed of a wrist independently. It is a third object of the present invention to provide a testing device whose racket-holding part can hold a ball-hitting tool in a state similar to a state in which a person grips the ball-hitting tool.
To solve the above-described problem, there is provided a testing device including a first joint extending upright from a base, a final joint on which a holder for holding a grip of a ball-hitting tool is installed, an intermediate joint disposed between the first and final joints. The first, intermediate, and final joints are successively connected to each other and rotated by individual driving devices in such a way that the ball-hitting tool held by the holder installed on the final joint is swung in X-, Y-, and Z-directions or/and rotated around a longitudinal axis of the baIl-hitting tool held by the holder to adjust/increase or decrease a distance, between a ball-hitting plane and the base, corresponding to a motion of a person swinging his/her arm up and down, with the person gripping the ball-hitting tool, adjust/change an angle of the ball-hitting plane corresponding to an inward rotation of the arm or an outward rotation thereof, and/or adjust/change an angle between a longitudinal axis of the ball-hitting tool and the base.
More specifically, the intermediate joint connected to the first and final joints having a swinging head respectively for swinging a body includes a lower arm joint (L-axis) connected to an upper end of the first joint (S1-axis) and swinging in a front-to-back direction; an upper arm joint (U-axis) connected to the lower arm joint (L-axis) and swinging in a vertical direction; a wrist joint (R-axis) connected to the upper arm joint (U-axis) and rotating on a longitudinal axis thereof; a wrist-swinging-joint (B-axis) connected to one end of the wrist joint (R-axis) and rotating in a vertical direction; and a wrist-rotation-joint (T1-axis) connected to the wrist-swinging joint (B-axis) and swinging in a left-to-right direction.
Further, a wrist-speed-increase-rotation-joint (T2-axis) swinging horizontally is provided on the wrist-rotation-joint (T1-axis) as the final joint; an extension plate is installed on the final joint; and the holder for holding the ball-hitting tool consisting of a tennis racket is held on one end of the extension plate (claim 2).
Let it be supposed that the ball-hitting tool testing device having the above-described construction is used as a testing equipment for a tennis racket. In this case, the testing equipment has the rotation shaft which rotates in a vertical direction, the rotation shaft corresponding to an inward rotation and outward rotation of a person""s arm, and the rotation shaft that can change the angle of the longitudinal axis of the tennis racket to the ground. Thus the testing device can reproduce a several ball-hitting motion including a spin-giving motion in a stroke or a serve and a volley similar to that in an actual play.
Further since the joints are driven by separate driving devices (motors), the rotation speeds of the joints can be adjusted separately. Thus it is possible to reproduce the characteristics of swings different from each other depending on a player. It is also possible to adjust the rotation speed of the entire testing device and the rotation speed of the joint corresponding to a player""s wrist independently. Therefore, it is possible to adjust the ball collision speed and the angular velocity of the wrist independently and freely.
The holder for holding the ball-hitting tool is fixed to a free end of an extension plate mounted on the final joint. Thereby it is possible to allow the rotation radius of the ball-hitting tool held by the holder and the head speed of the ball-hitting tool to be high.
Since the intermediate joints rotate simultaneously in the X-direction, the Y-direction, and the Z-direction, it is possible to reproduce an operation corresponding to a swing-up motion and a swing-down motion of an arm holding the ball-hitting tool. The operation is performed by adjusting/increasing or decreasing the distance between the ball-hitting plane and the base (ground). It is necessary for the ball-hitting tool testing equipment to perform an operation (swing) in such a way that a swing-up angle or a swing-down angle, namely, a straight line connecting a swing start point and a swing finish point to each other forms an angle of in the range of xe2x88x9210xc2x0xcx9c+10xc2x0 to the ground. Favorably in the range of xe2x88x9240xc2x0xcx9c+40xc2x0. More favorably in the range of xe2x88x9270xc2x0xcx9c+70xc2x0.
Further since the ball-hitting tool testing device has a function of rotating the ball-hitting tool, with the longitudinal direction thereof set as the axis of rotation, a function corresponding to inward and outward rotation of a player""s arm can be reproduced. This operation can be performed by adjusting/varying an angle of the ball-hitting plane. The angle range of the ball-hitting plane can be adjusted/varied favorably in the range of xe2x88x9230xc2x0xcx9c+30xc2x0 and more favorably in the range of xe2x88x9245xc2x0xcx9c+45xc2x0.
The ball-hitting tool testing device also has a function of altering an angle between the axis of the ball-hitting tool in its longitudinal direction and the base (ground). It is favorable to adjust/vary the angle in the range of xe2x88x9210xc2x0xcx9c+10xc2x0. It is more favorable to adjust/vary the angle xcex1 in the range of xe2x88x9245xc2x0xcx9c+135xc2x0. It is most favorable to adjust/vary the angle xcex1 in the range of xe2x88x9255xc2x0xcx9c+215xc2x0.
The intermediate joint is rotatably installed on an upper portion of the first joint and includes a speed increase joint (S2-axis) that is rotated by a rotation driving device separate from that of the first joint, and the head speed of the ball-hitting tool held by the final joint can be adjusted in the range of 5 m/sec-50 m/sec. Therefore the testing device is capable of coping with the head speed at the time when a high-class player hits a ball as well as to a head speed at the time when a beginner hits the ball.
Further the holder installed on the final joint includes an elastic sheet disposed along an inner peripheral surface of a cylindrical portion consisting of a rigid body in such way that the elastic sheet contains an air layer inward therefrom to allow the elastic sheet to grip the ball-hitting tool inserted into a bore of the cylindrical portion by injecting air into the air layer and inflating the elastic sheet; and a force for holding the holder is set to a range of 0.5-5 kgf/cm2.
The reason the force for holding the holder is set to the range of 0.5-5 kgf/cm2 is as follows: If the force is less than 0.5 kgf/cm2, the tennis racket cannot be gripped firmly. On the other hand, if the force is more than 5 kgf/cm2, an abnormal strain is generated on the tennis racket because the force exceeds a pressure at which a person grips the tennis racket.
More specifically, the elastic sheet disposed along the inner peripheral surface of the cylindrical portion in such way that the elastic sheet contains the air layer inward therefrom consists of an elastic tube having a hollow peripheral wall bonded to the inner peripheral surface of the cylindrical portion. An air injection path is formed on a peripheral wall of the cylindrical portion and a peripheral wall of the elastic tube in such a way that the air injection path penetrates through the peripheral wall of the cylindrical portion and the peripheral wall of the elastic tube. A check valve is provided inside the air injection path to seal air injected into the elastic tube.
The elastic tube is inserted into the bore of the cylindrical portion and an extra portion of the elastic tube projecting from an opening at the upper and lower ends of the cylindrical portion is folded. The folded portion is fixed to the peripheral surface of the cylindrical portion. Thereby it is possible to obtain the elastic sheet disposed along the inner peripheral surface of the cylindrical portion in such way that the elastic sheet contains the air layer inward therefrom. The air injection path communicating with the gap between the inner peripheral surface of the cylindrical portion and the elastic tube is formed on the peripheral surface of the cylindrical portion. The check valve is provided inside the air injection path to seal air injected into the gap from outside.
In the holder, since the ball-hitting tool is gripped with the elastic sheet (elastic tube) inflated with an air pressure. Thus the ball-hitting tool-gripping state is similar to the state in which a person grips it with her/his hand. That is, because the ball-hitting tool is gripped with the elastic force of the elastic sheet and the air pressure, the elastic sheet deforms greatly when a ball collides with the ball-hitting tool gripped in this way. Thereby the gripped ball-batting implement moves greatly. Therefore when the ball is hit with a tennis racket gripped in this way, it is possible to effectively lessen an impact force generated when the ball is hit and eliminate a disadvantage that a strain concentrates on the shaft and throat of the tennis racket.